Isotopic dilution studies of the chloroform–chloroform-d system by Raman difference spectroscopy

Raman difference spectroscopy has been used to measure small frequency shifts in the ν1 and ν2 bands of CHCl3 and CDCl3 in various mixtures of liquid chloroform and deuterochloroform. The frequency shifts relative to the pure liquids vary linearly with concentration, and at infinitive dilution are determined to be for CHCl3: Δν1=+0.56 and Δν2=+1.92 cm−1; and for CDCl3: Δν1=+0.33 and Δν2=+1.82 cm−1. The fact that all frequency shifts are positive indicates that an exchange effect between like molecules is responsible for the phenomenon. The ν4 bands show no frequency shifts but narrow substantially in bandwidth upon isotopic dilution. The position of the composite (CHCl3+CDCl3) ν6 band relative to the pure liquids was also measured as a function of concentration. The data confirm that the frequency difference between this band in liquid CHCl3 and in CDCl3 is 1.05 cm−1. The ν6 frequency appear not to be significantly shifted by isotopic dilution.